How Off-shore Wind Farms Work

When air flows over open water, it tends to move more quickly because there are no physical barriers, such as trees and mountains. As a result, the wind blows more steadily. And for that reason, off-shore wind turbines hold great potential for the future of wind energy production.

Still, the off-shore wind energy market represents a small fraction of the world’s wind industry because of the additional cost and risk of erecting turbines in open water. While some off-shore farms are being planned in the Great Lakes, the west coast of Canada and the Atlantic coast of the United States, most completed installations can be found in the North Sea, off the coasts of Denmark, Germany and the Scotland.

As of 2008, there were just over 500 off-shore turbines, representing about 1,100 MW of generating capacity. Ninety percent is produced by Denmark. Indeed, the world’s largest off-shore wind farms are known as Horns Rev I and II, located between 14 and 20 kilometres from the west coast of Denmark’s Jutland peninsula.

Typically, off-shore farms are located several kilometres away from the coast, in water that is up to 30 metres deep. The turbines tend to be larger – with higher towers and longer blades -- than their terrestrial counterparts. The additional size is meant to compensate for the extra expense of anchoring the foundations to the sea floor – anywhere from 30 to 70% of the total cost.

The construction techniques are identical to those used for building off-shore oil/gas drilling platforms, and involve driving steel poles deep into the sea bed. But the turbines themselves must be designed to withstand “stress loads” from high winds, tides and ice accumulation. Another complication is that off-shore wind turbines must be linked by underwater power lines to substations on the coast.

It will likely be years before off-shore wind energy becomes as widespread as onshore wind. But in smaller countries such as Denmark, the UK and the Netherlands where there is less space to build conventional wind farms, energy planners are increasingly looking to off-shore farms to provide future renewable power.